To solve the problems in current road traffics, there have been various efforts for development of the so-called Intelligent Road Traffic System (described as ITS hereinafter). Feasibility of the ITS have been examined in various countries, and in Japan there is the Vehicle Information and Communication System (described as VICS hereinafter), which has been put into practical use. Also test use of the Electronic Toll Collection (described as ETC hereinafter) will be started in the near future. The VICS is positioned as a more advanced version of a navigation system, and with the VICS it is possible to provide detailed information such as information on traffic jam, information concerning a time required to reach a destination, or information on traffic troubles. Also with the ETC, it is possible for a driver to pay a fee for an express-highway without stopping by executing radio communications between the driver's vehicle and the ETC or a toll-booth and electronically paying the fee. Details of these systems are disclosed in a web site on Internet (for instance, URL: http//www.moc.go.jp/road/road/h9point/2-2.htm).
As a further advanced version of ITS, now the possibility of realization of a more sophisticated Advanced-cruise-assist Highway System (described as AHS hereinafter) is now under examination, and in order to realize the advanced service as described above, it is necessary to provide various types of information concerning traffics and road management to discrete vehicles in a wide area. In the case of VICS, information is provided by wide area communications, but still communications with each discrete vehicle required for automatic driving has not been realized. The ETC is installed at a tool-booth and can provide communications with discrete vehicles, but only in a limited area.
Specific requirements for realization of the AHS will be studied in the future, for the most urgent and important objective to be achieved in the traffic control/management system is to prevent generation of a traffic accident which might be evaded with appropriate countermeasures, and more specifically it is now required to construct a system which can provide detailed information required to prevention of traffic accidents to each discrete vehicle. For instance it is clear that a chain-reaction traffic accident can be prevented or a gravity of the accident can be mitigated, when a traffic accident is caused by a car, if drivers of following cars know the accident. When a traffic accident or the like occurs, a traffic jam occurs, and in that case, if it is possible to provide information useful not only for grasping general information of the site of traffic accident, but also for making determination as to whether each driver should select another route for going around the site or should put up with the jam with a broadcasting type of communication system, it would be very effective for preventing generation of a traffic jam or for preventing a traffic jam from escalating into a large-scale one. Namely, it has been desired to develop a system capable of providing controls over the entire road network, when the system detects a state of a road or the like, by processing the information into that suited to each discrete vehicle and supplying the customized information to each discrete vehicles.
It is necessary to deliver information, which is to be supplied to a driver of a vehicle running on a road, as that based on positional data. For instance, it is necessary to deliver information such as "A traffic accident has occurred at point A, and a traffic jam is extending up to point B", or "A landslip has occurred at point C, and drivers are asked to go around through point D", or "Mist has been generated at around point E, and visibility is poor" to each driver on the road. In the examples above, the former two examples are cases concerning local events, while the last one is information on whether conditions and the information relates to a substantially wide area. As described above, all of information based on positional data can not always be treated in the same manner, and to provide detailed information satisfying each driver's need, it is important to clarify a positional relation between an event causing a trouble on a road and a vehicle's driver who receives the information. Namely, it is important to deliver appropriate information corresponding to a vehicle's position and also corresponding to a gravity of the trouble. Realization of a traffic control/management system and road information communicating system satisfying the requirements as described above is one of the objects of the present invention.
In a case of a chain-reaction traffic accident, drivers of vehicles running near and toward the site can prevent generation of a secondary traffic accident by knowing generation of the accident as early as possible, so that the information is urgent and important, but the importance becomes lower to vehicles running at positions slightly afar from the site. To vehicles running at positions further distant from the site of traffic accident, general information such as that concerning a type of traffic accident is enough.
It is an object of the present invention to realize a road information communicating system which can provide information concerning a situation on a road network to drivers by changing contents of the information according to each driver's position.
Further if information on various types of event is transmitted, even though a volume of each information is small, communication traffics in the entire road information communicating system is quite large, so that it is necessary to realize a transfer system or a transfer method capable of preventing increase of data traffic, and it is another object of the present invention to provide a road information transfer system or road information communicating system satisfying the needs as described above.